Use of imaging sensors or ultrasonic sensors or radar sensors in vehicle sensing systems is common and known. Examples of such known systems are described in U.S. Pat. Nos. 8,013,780 and 5,949,331 and/or U.S. publication No. US-2010-0245066 and/or International Publication No. WO 2011/090484, which are hereby incorporated herein by reference in their entireties.
Ultrasonic sensors and system have been used for over twenty years for detection of objects in close proximity to the front and rear of vehicles. In order to provide coverage across the entire area forward or rearward of the vehicle, sensors are typically spaced between 50-90 cm apart across the front and rear bumpers of the vehicle. Through the use of triangulation, the ultrasonic signal transmitted by a single sensor may be received by any of the sensors, including the sensor originally transmitting. Ultrasonic sensors typically are unable to detect objects closer than 17 cm from the sensor. This relates to the sensor being used as both transmitter and receiver. The sensor's settling time, (the duration required for vibration of the transducer to end after the end of the transmit cycle), is about 1 ms. During this time, the sensor is unable to detect objects. Advanced electronic methods have recently decreased this range where objects cannot be detected to 10 cm, for large objects exceeding the residual vibrations magnitude within the last 0.4 ms of the settling time. Systems are unable to report objects closer than this range.